Texas Instruments LMX2492 User manual

LMX2492 Evaluation Instructions
Ultra Low Noise Frequency Synthesizer with
Integrated VCO Evaluation Board Operating
Instructions
User's Guide
Literature Number: SNAU160C
March 2014–Revised November 2014

Contents
1 Evaluation Board Setup ........................................................................................................ 4
1.1 Evaluation Board Setup Diagram and Connections..................................................................... 4
1.1.1 VCO Outputs ........................................................................................................ 4
1.1.2 VCC 5V .............................................................................................................. 4
1.1.3 VCC 3P3V ........................................................................................................... 4
1.1.4 USB2ANY Connector .............................................................................................. 4
1.1.5 OSCin/OSCin*....................................................................................................... 4
2 Evaluation Board Configuration............................................................................................. 5
2.1 Loop Filter Configuration.................................................................................................... 5
2.2 CodeLoader Software Settings ............................................................................................ 6
2.2.1 Port Setup ........................................................................................................... 6
2.2.2 Device Selection .................................................................................................... 7
2.2.3 Bits/Pins Tab and Restoring the Default Configuration........................................................ 8
2.2.4 Registers Tab ....................................................................................................... 9
2.2.5 PLL Frequency Tab............................................................................................... 10
2.2.6 Ramp Generator Tab ............................................................................................. 11
3 Schematic ......................................................................................................................... 12
4 Board Layers Stackup......................................................................................................... 13
5 Bill of Materials .................................................................................................................. 14
6 Typical Performance Measurements..................................................................................... 16
6.1 PLL Phase Noise........................................................................................................... 16
6.2 Ramping Example.......................................................................................................... 19
Revision History.......................................................................................................................... 20
2Contents SNAU160C–March 2014–Revised November 2014
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User's Guide
SNAU160C–March 2014–Revised November 2014
Evaluation Board Operating Instructions
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Direct VCO Output (~10 GHz)
VCO/2 Output (~5 GHz) 5V Supply
Optional:
3V Supply
Optional:
VCO/4 Output
Optional:
Single Ended or
Differential
Reference Signal
USB2ANY
Connector
Chapter 1
SNAU160C–March 2014–Revised November 2014
Evaluation Board Setup
1.1 Evaluation Board Setup Diagram and Connections
Figure 1-1. Evaluation Board Connection Diagram
1.1.1 VCO Outputs
The LMX2492 operates at 10 GHz, but this can be a problem for some test equipment. If it is, use the
VCO/2 output or the VCO/4 output. The VCO/4 output is powered down by default, but can be configured
if necessary.
1.1.2 VCC 5V
The board operates on 5V and regulates this down to 3.3 V for the PLL. The board can be configured to
operate wit separate
1.1.3 VCC 3P3V
This is actually supplied from the regular off the 5V supply, but can also be run from a 3.3 V supply if the
regulator is disconnected and a few resistors are changed.
1.1.4 USB2ANY Connector
Connect the board to the computer using the USB2ANY connector, which comes supplied with the kit.
1.1.5 OSCin/OSCin*
The board has an on board XO, but the OSCin pins can be run either single-ended or differentially.
4Evaluation Board Setup SNAU160C–March 2014–Revised November 2014
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Chapter 2
SNAU160C–March 2014–Revised November 2014
Evaluation Board Configuration
2.1 Loop Filter Configuration
Table 2-1. Loop Filter Values
PARAMETER LMX2492
VCO Frequency 9.4 – 10.1 GHz
VCO Gain (MHz/V) 200 MHz/V
C1_LF 68 pF
C2_LF 3.9 nF
C3_LF 150 pF
C4_LF Open
R2 390 Ω
R3_LF 150 Ω
R4_LF 0 Ω
Charge Pump Gain 3.1 mA
Phase Detector Frequency 100 MHz
OSCin Frequency 100 MHz
5
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CodeLoader Software Settings www.ti.com
2.2 CodeLoader Software Settings
The CodeLoader software is used for programming this device and is available at www.ti.com/codeloader.
2.2.1 Port Setup
The port setup shows which pins are sent to the pins of the header. If using the USB2ANY board, it is
recommended to click the "Identify" button and ensure the LED light is blinking to ensure that this is
working correctly. Note that position 3 is MUXout, which can be used for readback. In order to do this, the
MUXout pin needs to be programmed to Readback and also resistor R68 needs to be placed.
Figure 2-1. LMX2492 Port Setup
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2.2.2 Device Selection
Go to “Select Device” →“PLL–Fractional” →LMX2492
Figure 2-2. Part Selection
7
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CodeLoader Software Settings www.ti.com
2.2.3 Bits/Pins Tab and Restoring the Default Configuration
The Bits/Pins tab shows the state of the programming fields. Note the scroll bar at the bottom. One can
right mouse click on any field for a short description of what it does. To restore the part to the original
software configuration, on can select the default mode as shown.
Figure 2-3. Restoring Default Mode
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2.2.4 Registers Tab
The registers tab is not necessary to program the part, but it does show the regsiters. The LMX2492 also
supports readback. To use this, set the MUXout pin to readback and attach resistor R68 to connect this
pin back to the programming header. Once this is done entire registers can be read, or a specific field can
be typed in to read the value. Realize that some fields of the LMX2492 are read only and therefore might
not be the same as written to.
Figure 2-4. Registers Tab
9
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2.2.5 PLL Frequency Tab
Verify your “PLL” Tab looks like below:
Figure 2-5. PLL Frequency Tab
10 Evaluation Board Configuration SNAU160C–March 2014–Revised November 2014
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